The invention relates to flexible armored cable; and more particularly to such a cable for electric wires and the like, having a spiral armoring made of zinc plated steel. Such cables are used, for example, for electrical power transmission and for telecommunications.
Cables of this general type are constructed from a cable core, containing one or more insulated conductors, and one or more protective layers around the core. The protective layer may be manufactured from a variety of materials, such as synthetic resins or jute impregnated with bitumen, or may consist of an inner cover and a sheath. A combination of materials may be used, and to provide protection against mechanical loads and abrasion, and extra protective armoring layer is frequently provided. A common, known armor consists of one or more steel tapes or bands wound helicoidally around the cable core, and usually in turn covered by a sheath, to protect against corrosion, such that the steel tape or band does not form the outside of the cable. Nonetheless, as a result of abrasion or accident, the sheath is sometimes damaged such that the armor becomes exposed.
To avoid corrosion of the armor, even where an outer sheath is to be applied, the armor band is frequently made of a zinc-plated steel such as that prescribed in the ASTM Standard ANSI/ASTM A 459-71 (Reapproved 1975). That standard prescribes the use of thermally zinc-plated steel which is plated on all its surfaces including the edges. Because steel band is usually manufactured by cutting (slitting) or punching from steel sheet, compliance with this Standard requires that the zinc plating follow the cutting or punching operation. However, it is more economical to zinc-plate entire sheets rather than the narrow band. The usual thermally zinc-plated steel band also has the disadvantage that, upon winding the steel band around the cable core, the zinc often scales partly or entirely.
Another method of providing corrosion resistance, known from British Patent Application No. 2,060,726A, involves the use of zinc wire in a cable to protect a steel wire armoring. However, this is a relatively expensive technique that produces poorer mechanical protection.